The present invention relates to an engine control apparatus, and more preferably to an engine control apparatus adapted to detect fuel property and a residual fuel quantity in an engine and control the engine optimally on the basis of detected information.
As the emission regulations on automobile engines being tightened in Japan, North America and Europe in recent years, there has been requirement for greater improvement in the emission performance (exhaust emission characteristics) of the engines. With the emergence of high-performance catalysts and the remarkable advances in precision in catalyst control, the exhaust emission is discharged in largest quantities from the engine chiefly when the engine is started. On the other hand, when the engine is at rest, a certain amount of fuel is left behind in the intake passages and the cylinders (engine). The fuel which leaks from the fuel injection valve while the engine is at rest remains in the intake passage and the cylinder. Because the residual fuel burns together with fuel supplied from the fuel injection valve when the engine is started, the residual fuel acts as a disturbance to start-up control, and degrades the emission performance.
Generally, fuels show a certain extent of variation in their property, and the evaporation rate at low temperature varies with their properties. Since the optimum fuel quantity at engine start-up changes with different fuel evaporation rates, a number of methods have been proposed for fuel property detection, but in most of those methods, the fuel property is detected during a start-up of the engine from a point of view of early-stage detection. Here again, the residual fuel is a major disturbance to detection of fuel property.
In Patent Document JP-A-7-27010, there is disclosed an engine control apparatus which detects a change rate ΔNe of engine revolution speed, and determines the heaviness of fuel based on ΔNe and charge efficiency with reference to a map made up of water temperature, intake air temperature, and atmospheric pressure. This control apparatus operates on a principle that by detecting ΔNe, namely, a combustion torque, a fuel evaporation rate (burned fuel quantity or air-fuel ratio in combustion) is obtained, and a fuel property is detected indirectly according to the fuel evaporation rate.
Patent Document JP-A-8-177556 reveals a control apparatus in which an evaporation time constant τ representing a temporal change in fuel quantity sucked from the inlet system into the cylinder (combustion chamber) of the engine is calculated based on an evaporation rate time constantτ0 at a reference engine revolution speed and a reference engine load.
In this control apparatus, there is proposed a method, which applies low load to the computer dedicated to control, for calculating with high precision a fuel remaining in the intake port without being sucked in the combustion chamber when the fuel is injected during engine operation.
Further, the Patent document JP-A-2001-107795 discloses a control apparatus which determines a fuel property on the basis of a relation between a fuel injection quantity or a parameter correlated with the fuel injection quantity and a fuel combustion quantity or a parameter correlated with the fuel burned quantity when a predetermined condition is established (during idle operation, for instance).